Blue Square Electrical Control System
Engine Control Relay Panel
One was provided per engine. Normally these were located on the underframe, some types such as Met-Camms could have them inside the vehicle.
The relay board was manufactered by J. Stone & Co. (Deptford) Ltd. but supplied by B.U.T.
Description
From the BUT 50000 Series Service Manual:
The engine control box contains three Tonum type relays mounted on an ebony insulated panel and may be readily identified, the specification numbers being stamped on plates attached to each unit.
The relays are mounted horizontally so that the contact faces are in a vertical plane, thereby ensuring that no dust will collect on the faces.
One relay (specification T3633) consists of one pair of normally open main contacts and two pairs of normally open auxiliary arcing contacts which are connected in series.
These are often referred to as the "sparking tips" and are accordingly arranged to "make" a fraction before and "break" a fraction after the main contacts.
The two other relays (specification T3500) consist of one pair of normally closed main contacts.
Schematic
This shows the connections to the panel, taken from the BUT 50000 Series Service Manual.